Medium-spin states in Cs-135
Limited information is currently known on medium-and higher-spin states for Cs-135, a neutron-rich nucleus amenable to shell-model calculations due to its proximity to the shell closures in Sn-132. In order to extend the level structure of Cs-135 to higher excitations, this nucleus was studied via prompt gamma-ray spectroscopy of fragments following the fission of the compound nucleus Th-226 formed in the O-18 (91 MeV) + Pb-208 fusion-fission reaction. Medium-spin states up to spin (23/2) and similar to 3.3 MeV excitation energy have been established. The observed states were compared with those in the neighboring N = 82(137)Cs nucleus, as well as with states in the neighboring N = 80 isotones. The coupling of the odd proton occupying the g(7/2) orbital to the yrast states in the Xe-134 and Ba-136 cores could account for the lower excited states of Cs-135. The experimental results are compared with predictions from shell-model calculations.